This page lets you exclude the viewer pane from displaying files in certain folders.
Click Add folder to add a specific folder. Selecting files within this folder won't trigger the viewer pane.
Click Add Wildcard to use a wildcard pattern. This can match particular folders (e.g. \\* would match all network paths) and it also lets you exclude certain filetypes wherever they're located. For example, *.pdf would prevent the viewer pane from showing PDF files.